The present invention generally relates to unmanned aircrafts for image acquisition applications like for instance digital terrain modelling, i.e. the digital production of topographic maps used for infrastructure planning like mines, volume calculation of large deposits such as dredge deposits, urban construction planning, land reclamation or vegetation monitoring in the agro-industry, etc. The unmanned aircraft with wing according to the current invention is also useful in other applications, like for instance real-time surveillance. The invention in particular concerns efficient production of a safe, impact resistant, and disposable wing for such unmanned aircrafts.
Topographic data that are essential for planning and decision making in various applications can be collected either manually through on-site measurements using Global Positioning System (GPS) transceivers, photogrammetry, terrestrial scanners, LIDAR technology, or via image acquisition using a high resolution digital camera aboard a small unmanned aircraft system (UAS). Usually, a grid density with decimetre accuracy or better is required.
Despite its limitations, terrestrial surveying is at present still the common approach for gathering elevation data of a terrain that has to be modelled. A ground surveyor can measure a few tens or even hundreds of points a day using state of the art GPS technology. Such manual, on-site surveying however requires a human accessible terrain and may be dangerous. The presence of the surveyor may conflict with ongoing operations and/or the surveyor may be at risk due to the nature of the terrain, e.g. a minefield, construction area, zone with collapsed buildings as a result of an explosion, etc. The resolution that can be obtained with terrestrial topographic surveying is limited due to the inherent limited number of measurable points. The resolution or level of detail can only be increased by adding manual measurements. These manual measurements typically hit the boundaries of scalability when the project requires thousands or more points to be measured. The data acquisition effort increases linearly with the expected resolution and with the size of the area that is surveyed. As a consequence, manual surveying on-site becomes too expensive and too time consuming in most cases.
LIDAR or LIght Detection And Ranging is an optical remote sensing technique that measures properties of scattered light in order to find the range of a distant target. Terrestrial LIDAR technology, e.g. a fixed scanner or mobile scanner, is bound to the same limits as the terrestrial surveyor. Moreover, image extraction for Digital Terrain Modelling is rather difficult due to the angle whereat the data are captured. Using an airplane or helicopter as moving platform, LIDAR allows 3D terrain mapping. The need for costly equipment such as an accurate Inertial Navigation System and the integration thereof in an aircraft, limits the applicability and market penetration of LIDAR.
As mentioned here above, an alternative to manual on-site measurements consists in image acquisition using an unmanned aircraft system (UAS) equipped with a high resolution camera. Such unmanned aircraft can scan a predefined area and real-time transmit the captured images, e.g. in case of surveillance, or locally store the captured images for later processing. From launch to landing, the flight can be conducted fully automatically. The unmanned aircraft has a typical flight altitude of 100 to 300 m, has a typical coverage of a few km2, and has digital cameras aboard that enable to model the terrain with centimetre resolution. As a consequence, the unmanned aircraft may collect data on a few hundred thousands of measurement points during a single flight of for instance 30 minutes. The unmanned aircraft scans the terrain that has to be modelled through parallel sweeps and consecutive, overlapping camera shots. A ground control station can monitor the flight and eventually also performs a remote image quality check. In case of topographic mapping, the collected data is a set of pictures tagged with GPS coordinates of the respective locations where the pictures were taken. The number of pictures obviously depends on the size of the terrain and the required resolution.
The technical problems where designers of small unmanned aircrafts for image acquisition applications cope with are size and weight, robustness, weather and wind sensitivity, impact resistance, lifetime, cost and complexity for mass production.
A prior art unmanned aircraft for remote image acquisition is the Airborne Vehicle System (AVS) from Air Robotics. The AVS is described and pictured in various press releases, starting 5 Aug. 2009. These press releases can be retrieved from the Internet via the following URL:
http://airrobotics.wordpress.com/
The AVS can carry electro-optical, infrared and chemical sensors to provide real-time images of an area for surveillance and reconnaissance applications. In order to make the AVS impact tolerant, Air Robotics has developed a fuselage and tail group out of lightweight, energy dissipating materials. As is illustrated by the press release of 7 Aug. 2009, the AVS consists of a foam core that is cut—i.e. a moldless construction method—and a protective sheet or layer. The lightweight foam enables the AVS to carry a heavier payload while surviving crashes.
Air Robotics' AVS is disadvantageous for several reasons. Firstly, cutting a foam core, as is required in Air Robotics' moldless construction method, requires time-consuming, manual production steps. Airborne's AVS in other words cannot be manufactured efficiently in large volumes. In particular, the application of a protective sheet or laminate covering the core foam of the AVS is a time-consuming step that complicates the production process. Moreover, this laminate or protective cover renders the AVS unsafe when used in civil areas. Although Airborne's unmanned aircraft seems to survive a crash test, a human being, animal or object hit by the AVS in case of a crash, will not survive or at least be heavily injured as a result of the impact of the hard external layer. Further, Airborne's laminated foam core does not allow recovering the expensive electronics inside, like for instance the high resolution digital camera, the battery, etc. Whereas the lifetime of the wing may be expected to be limited to a few tens of flights, e.g. 20 to 50 flights, the expensive electronics carried by the unmanned aircraft will have a typical lifetime that is at least a tenfold thereof. Since batteries can be recharged more than thousand times, digital cameras have a life duration of more than thousand hours of operation, and control electronics even have lifetimes of 10.000 hours or more, the electronics inside an unmanned aircraft for image acquisition applications can at present safely survive hundreds, possibly even thousands of flights.
In summary, Air Robotics' AVS is complex and expensive to manufacture, cannot be used safely in civil environments, and does not allow recovery of the expensive electronics inside for reuse as long as their lifetime permits.
The PCT Patent Application WO 2004/060743 from the University of Florida, published on 22 Jul. 2004 and entitled “Bendable Wing for Micro Air Vehicle” describes another wing for an unmanned aircraft that is designed to be outfitted with still frame cameras and video cameras for image acquisition in military applications. As is illustrated by FIG. 1 of WO 2004/060743, the wing consists of a ribbed support structure covered by a layer or sheet of resilient material such as latex. This way, the wing is designed to resist flexing upwards during a flight, and is bendable downward in such manner that the aircraft can be stored in a compact cylindrical volume that is carried by military personnel, for instance in their backpack.
Just like Air Robotics' AVS, the wing known from WO 2004/060743 is complex to manufacture. Each rib of the support structure has to describe the exact shape of the airplane and therefore has to be produced manually. Although the unmanned airplane based on the known wing is foldable, it is not impact resistant and also not safe for use in civil environments. The thin latex layer or alternate resilient sheet does not protect a human being or any other object that is hit by a crashing plane from being injured heavily. Further, the wing cannot be removed easily thereby saving expensive electronic components inside the aircraft for reuse.
U.S. Patent Application Ser. No. US 2004/0195438 describes a light weight and impact resistant flying wing toy made out expanded polypropylene (EPP). The airframe stiffness is increased through one or more spar shafts that are embedded inside the EPP wings, e.g. an elongated wing stiffening spar 20 that is mounted inside the wing.
The flying wing toy known from US 2004/0195438 is rather complex to produce. Typically, the wings are cut out of an EPP core in a moldless step that is time-consuming and labour-intensive. Thereafter, as mentioned in paragraph [0044] of US 2004/0195438, holes are drilled in the EPP wings to enable the stiffening spar 20 to be mounted. The drilling and mounting of the spar constitute additional steps that complicate mass-production of the flying wing toy. A further disadvantage of drilling holes in EPP and passing a spar therethrough is the unavoidable absence of adhesion between the EPP granules and the spar. As a consequence thereof, the spar shall be able to swivel or rotate resulting in non-optimal strength, rigidity, and torsion stiffness of the flying wing toy.
It is further noticed that the flying wing toy known from US 2004/0195438 is not adapted for image acquisition or surveillance application. It does not have a container to hold image acquisition or surveillance electronics, is therefore more lightweight by nature, and consequently does not suffer from safety and impact resistance constraints that are comparable to those faced by unmanned aircrafts used for image acquisition and surveillance applications.
An additional consequence of the fact that this wing toy is not adapted for image acquisition or surveillance applications, is that the flying wing toy known from US 2004/0195438 is not designed to be removable and replaceable with reuse of electronics.
French Patent Application FR 2 920 745 entitled “Drone Modulaire a Sous-Ensembles Détachables” describes an unmanned aircraft that comprises wings (2 in FIG. 1) made of expanded polypropylene and an elongated stiffness bar (34 in FIG. 2). The unmanned aircraft is designed for image acquisition applications with a container for holding image acquisition electronics (5 in FIG. 2). The aircraft known from FR 2 920 745 contains a multiple of components, some of which are detachable for transport, like the wings. These detachable components render the aircraft less robust and complex to produce.
The production process for the aircraft is complex and time consuming in general. Just like the wing toy known from US 2004/0195438, the wings are cut out of an EPP core, typically through a hot-wire process, and the stiffness bar is placed after a hole is drilled in the EPP wings. These steps typically require manual handling and are therefore not suitable for mass production.
The elongated bar 34 increases the torsion stiffness of the aircraft but does not constitute a support structure that prevents all types of deformation. The adhesion between the stiffness bar and EPP granules of the wings is poor as a result of the production process. The stiffness bar therefore can swivel or rotate.
It is an objective of the present invention to provide a wing for an unmanned aircraft used in image acquisition applications that overcomes the above mentioned shortcomings of the prior art solutions. More specifically, it is an objective to disclose a wing that can be produced at low cost and complexity in large volumes. It is a further objective of the current invention to disclose a wing and unmanned aircraft that are impact resistant and safe for use in civil neighbourhoods. It is a further objective of the invention to disclose a low cost wing that is easily removable and disposable thereby enabling reuse of expensive electronic components such as cameras, batteries, etc. that typically have a larger lifetime than the wing.